Proton Transfer via Arginine with Suppressed pKa Mediates Catalysis by Gentisate and Salicylate Dioxygenase.
J Phys Chem B
; 128(28): 6797-6805, 2024 Jul 18.
Article
em En
| MEDLINE
| ID: mdl-38978492
ABSTRACT
Gentisate and salicylate 1,2-dioxygenases (GDO and SDO) facilitate aerobic degradation of aromatic rings by inserting both atoms of dioxygen into their substrates, thereby participating in global carbon cycling. The role of acid-base catalysts in the reaction cycles of these enzymes is debatable. We present evidence of the participation of a proton shuffler during catalysis by GDO and SDO. The pH dependence of Michaelis-Menten parameters demonstrates that a single proton transfer is mandatory for the catalysis. Measurements at variable temperatures and pHs were used to determine the standard enthalpy of ionization (ΔHion°) of 51 kJ/mol for the proton transfer event. Although the observed apparent pKa in the range of 6.0-7.0 for substrates of both enzymes is highly suggestive of a histidine residue, ΔHion° establishes an arginine residue as the likely proton source, providing phylogenetic relevance for this strictly conserved residue in the GDO family. We propose that the atypical 3-histidine ferrous binding scaffold of GDOs contributes to the suppression of arginine pKa and provides support for this argument by employing a 2-histidine-1-carboxylate variant of the enzyme that exhibits elevated pKa. A reaction mechanism considering the role of the proton source in stabilizing key reaction intermediates is proposed.
Texto completo:
1
Base de dados:
MEDLINE
Assunto principal:
Arginina
/
Prótons
Idioma:
En
Revista:
J Phys Chem B
Assunto da revista:
QUIMICA
Ano de publicação:
2024
Tipo de documento:
Article
País de afiliação:
Estados Unidos